A wet processing apparatus is known as an apparatus for processing a substrate, such as a wafer. An electroplating apparatus, an electroless plating apparatus, and a wet etching apparatus are examples of the wet processing apparatus. Such wet processing apparatus generally includes a processing bath for holding a processing liquid therein for processing a substrate, and a rinsing bath for holding a rinsing liquid therein for cleaning the processed substrate. The substrate is immersed in the processing liquid held in the processing bath, so that the substrate is processed. Thereafter, the substrate is transported to the rinsing bath, and is immersed in the rinsing liquid held in the rinsing bath, so that the substrate is cleaned (or rinsed). Hereinafter, the rinsing bath will be described with reference to FIG. 8.
FIG. 8 is a view showing a typical rinsing bath. As shown in FIG. 8, the rinsing bath includes an inner bath 101 for holding the rinsing liquid therein, and an overflow bath 102 surrounding the inner bath 101. A drain pipe 103 is coupled to a bottom of the overflow bath 102, and a discharge valve 104 is attached to the drain pipe 103. One end of a drain pipe 105 is coupled to a bottom of the inner bath 101, and other end of the drain pipe 105 is coupled to the drain pipe 103. A discharge valve 106 is attached to the drain pipe 105. The drain pipe 105 extends through the bottom of the overflow bath 102. In order to prevent a leakage of the rinsing liquid from the overflow bath 102, a packing 112 for sealing a gap between the bottom of the overflow bath 102 and the drain pipe 105 is provided.
A rinsing liquid supply pipe 110 for supplying the rinsing liquid is coupled to the bottom of the inner bath 101, and an on-off valve 111 is attached to the rinsing liquid supply pipe 110. When the on-off valve 111 is opened, the rinsing liquid is supplied through the rinsing liquid supply pipe 110 into the inner bath 101. With the discharge valve 106 closed, the rinsing liquid is gradually stored in the inner bath 101. The rinsing liquid stored in the inner bath 101 eventually overflows the inner bath 101 into the overflow bath 102.
A substrate W that has been processed in a processing bath (not shown) is transported to a predetermined position above the inner bath 101. With the on-off valve 111 opened, i.e., while the rinsing liquid is being supplied into the inner bath 101, the substrate W is immersed in the rinsing liquid retained in the inner bath 101, whereby the substrate W is cleaned (rinsed). The rinsing liquid overflows the inner bath 101 into the overflow bath 102 during cleaning of the substrate W. Further, the rinsing liquid in the overflow bath 102 is discharged through the drain pipe 103 to an exterior. After cleaning of the substrate W, the discharge valve 106 is opened, and the rinsing liquid stored in the inner bath 101 is discharged through the drain pipe 105 and the drain pipe 103 to the exterior.
A pamphlet of International Publication No. 00/070128 discloses a water-washing bath having a quick dump function provided in an electroplating apparatus. Further, Japanese laid-open patent publication No. 61-61425 discloses a water-washing bath having an inner bath and an overflow bath.
In the rinsing bath illustrated in FIG. 8, it is necessary to provide two drain pipes, i.e., the drain pipe 105 for discharging the rinsing liquid from the inner bath 101 and the drain pipe 103 for discharging the rinsing liquid from the overflow bath 102. Further, it is necessary to provide the drain pipes 103, 105 with the drain valves 104, 106, respectively. Therefore, a structure for discharging the rinsing liquid is complicated, and a large space is required for installing the drain pipes 103, 105 and the drain valves 104, 106.
Further, from a point in time when the rinsing liquid fills the inner bath 101 to a point in time when the substrate W is introduced into the inner bath 101, a large amount of the rinsing liquid, which does not contribute to cleaning of the substrate, is discharged through the drain pipe 103, and as a result, a total amount of the rinsing liquid used increases. Further, since an amount of the rinsing liquid that can be held by the inner bath 101 includes not only a volume of the inner bath 101 itself, but also a volume from the bottom of the inner bath 101 to the drain valve 106, more rinsing liquid than necessary is required. In order to reduce the amount of the rinsing liquid to be used, the supply of the rinsing liquid may be stopped by closing the on-off valve 111 until the substrate W is immersed in the rinsing liquid. However, if a flow of the rinsing liquid is stagnant, bacteria may be generated in a flow passage of the rinsing liquid, resulting in a contamination of the rinsing liquid.